As we all know small pistol primers Are nearly impossible to find and I have nearly none left. How much should I decrease my powder load to compensate for increased pressure from a magnum primer?

You can use them without adjusting your load on the face of it. They shouldn’t increase pressure, but since you are changing a component, you should restart building the load back up to your current powder charge (especially if it is close to a max load).

Depends on powder & cartridge. Despite what one would think, my testing with fast powders shows very little diff in vel, thus pressures when swapping std for mag. With slower powders, things are much diff. So it depends.
I have used mag primers in my 9mm minor loads with WST without changing anything. In my 357sig, mag primers under aa#9, vel, went up more thsn 100fps.

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NRA Cert. Inst. IDPA CSO

Once, in error, I kept grabbing boxes of Winchester primers (without noticing the were for Small Pistol Magnum) while priming a bunch of 38 Special cases...

Thankfully the vast majority of these were actually in nickel +P cases : I set them aside and have just loaded up the last of them with that Federal HST130gr JHPWC, so..

No real harm done?

Cheers!

P.S. Now I mark the Magnum primer boxes with a piece of red tape.

I don't think the magnum primers will hurt anything, but just as when changing ANY of the components of a load, best practice is to back off your usual load by 10% and work back up to it just to be sure.

As for myself, I discovered years ago that even in magnum loads I usually get more consistent (if usually very slightly slower) velocities with standard primers, so that's what I use for 'most everything.

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Pisgah

I've been using Small Pistol Magnum primers in all of my loads for the last 4-5 years. I try to use only Federal since some of my revolvers have light actions and won't think about firing CCI. I can't tell the difference in .38/.357 and 9mm. My .38 and 9mm are loaded light for target with Bullseye, Tightgroup and Universal. Before my chronograph got stolen I tried some magnum and non magnum loaded target loads and saw very little difference in velocity with very light charges. The only difference I "think" I've noticed is Bullseye seems to burn cleaner, but that might just be me. I don't plan to ever go back since its so convenient to just keep one type on hand.

Unless you are loading to maximum safe pressure, I don't think there is going to be a significant difference if you switch to small pistol magnum primers. If you are at or very near maximum, I'd back off a little and work up to a safe maximum load.

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VCDL, GOA, NRA

With the current primer shortage I bought some SPP's and LPP's in magnum because that's all that was available. I made up some test loads for my 9mm using Titegroup and .45 acp with CFE and chronoed them.

There was virtually no difference between the speeds with magnum primers vs standard ones in either caliber.

I won't tell anyone else what to do but for me I consider the standard and magnum primers interchangeable.

I don't load to mag pressures veery often and a fellow bought some Remington SPPMag primers(5 1/2s?). When he realized they were mag primers he gave 'em to me. Didn't make a bit of difference in my 38 sp loads. Heck I've been known to use SRPs in pistol loads too. Work fine. Top end loads always go by the recommended components

In my target loads, magnum primers average about 15 fps more velocity. This amount is barely noticeable since the difference between one round and another is often more than that. You have to chronograph a large sample of standard and magnum of the same load, then average them out to see it.

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protocalldesign.com

A lot depends on the cartridge you're loading, the powder and the charge .
But don't give out too many details ...makes answering a question too darn easy .
The only answer I can give is from 0% to 10% , all depending on unknown specific's .
Gary

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Certified Cajun
NRA Member

This question comes up very often. Maybe there should be a sticky about it. In short, for handgun loads, SP, SPM and SR primers are interchangeable, the only caution being that if your handgun has a weak firing pin strike, you may get occasional failures to fire if you use SPM or SR primers, as the primer cups are a little thicker metal. To find out, take at least 10 primed cases and see if they all fire in your gun. If there are no failures, reliability is probably OK. Ballistic performance differences will be negligible, if any. Changing loads is unnecessary.

I just back off .2 grains as a standard for less than max loads. That's just a principle because I 'changed components' for a recipe. I agree with others that it's not that big of a deal unless at max.

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"He was kinda funny lookin'"

I epuldnt say interchangable. If you are running a medium to slow powder, gping with a sm rifle or mag primer does increase vel, so I would also think pressures, everything else being the same. If you use a sm rifle primer to work your load ip, then yes, interchangable.

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NRA Cert. Inst. IDPA CSO

Today at my gun store.......
all they had was large pistol primers.

Looking pretty bad.

It depends on the manufacturer. The difference in Remington primers magnum vs. standard is the magnum cups are thicker to help with higher pressure in true magnum loads. Same charge of priming compound.
Being thicker they are harder to light. If you’ve put in lighter mainspring, you’ll have to change it back.

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and what his trumpet saith

Little to no decrease in powder charge is needed but as with all component changes you should work up the load again.

This question comes up weekly. Do a search and you will find more information that you will know what to do with lol.

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Freedom is never free!!
SWCA #3437

No one really knows how much "energy" there is in all the different primers. The primer companies do not publish any such data. Internet pictures of the flame length of a few different primers from years ago prove nothing.


In theory a mag primer has a bigger or hotter flash to ignite magnum primers. But what that does to non mag powders is a WAG without extensive testing with expensive equipment, control conditions and a whole bunch of different powders.


Then there are the different brands of primers, it is all anecdotal if one is "hotter" than the other. With LPP how can Winchester get by with just one primer for both Mag and regular loads??.


Bottom line, use what your have and do not use MAX loads at first (which you shouldn't anyway)

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Still Running Against the Wind

Generally, the only significant difference between a SP and the SPM and SR primers is the thickness of the primer cup, the purpose of which is to better withstand higher pressures of rifle and magnum pistol loads. And even that thickness varies among manufacturers. There are far better things to worry about than the differences between them. If a SPM or SR primer brand works reliably in your handgun, there is no reason not to use them.

Since my reloading supplier charges the same price for standard or magnun primers, I always went with the magnum primers, never noticed any difference, but I don't load at max either...use them, their fine.

Never seen a difference with 38 loads and magnum primers. The only magnums I reload are for my 77-357 rifle.

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Heavily armed old man.

The design of the MAGNUM primers means a longer spark (brisance) to better ignite harder to ignite magnum powders! This in itself doesn't mean higher pressure! People have reported all manner of differences when using magnum primers in non magnum powders. From higher to lower velocities to wider and narrower S/D!

As in the above my chrono only saw about +25 FPS with popular powders and 9mm Minor PF loads.

The same for 38 Spl. For 45ACP Winchester primers are LPP/LPPM loads!

As a reloading instructor I can only advise to use published recipes. As noted above start with reduced loads and work up if choosing to use SPPM primers!

Smiles,

Thanks for starting this thread.
I had the same question.

Due to lack of supply given current climate i have been using LMPP in my .45s with no noticeable difference... i recently was abil to source some standard LPP so ill use them in my 10s... if i ever have to run LMPP in my 10s ill approach max with caution

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This is the way....